A method of mounting a semiconductor laser element, and joining a photodiode to a copper heat sink using bonding bumps to optically align the semiconductor laser element and the photodiode with high precision is known (for example, refer to Japanese Unexamined Patent Application Publication No. H10-208269 (FIG. 1)).
In the method, in the case of joining the photodiode with the bonding bumps, the relationship between pressure applied to the bonding bumps and height of the bonding bumps deformed according to the applied pressure is examined in advance, and a proper application pressure is selected according to the relationship.